A surface of the initially described type is known from the AIAA Paper No. 83-0227, Bushnell, D. M. "Turbulent drag reduction for external flows". In this connection, fine longitudinal grooves extending in the direction of flow are provided, which are separated from one another by ribs having sharp edges and which reduce or even prevent transverse flow. The result of this is a surface which exhibits low resistance when turbulent flow takes place around the body.
From J. Fluid Mech. (1967), 30, pages 741-773, Kline, S. J., Reynolds, W. C., Schraub, F. A., Runstadler, P. W. "The sructure of turbulent boundary layers" it is known that the lowest layer, close to the wall, of a turbulent boundary layer, i.e, the viscous underlayer, exhibits in the direction of flow bands of reduced velocity, which can be designated as "slow bands". The "slow bands" are now and again swept up into a region of high velocity. This mechanism is an essential component of the turbulent exchange of pulses and generates the high flow resistance of a turbulent boundary layer.
If the "slow bands" are regarded as a secondary flow in the vicinity of the wall, which is caused by the alternating pressure distribution in the boundary layer, the measures for the reduction of the flow resistance should be aimed at obstructing or avoiding the formation of the "slow bands". The process by which the "slow bands" are produced is schematically illustrated in FIG. 1. A surface, over which turbulent flow takes place, of a body is represented; in this connection, the indicated velocity profiles may arise at a certain time. In a region of low pressure, slow fluid which flows along the surface of the body is aspirated and the result is a transverse flow, as a consequence of which the slow band is created. It is even possible that this slow band is swept upwardly, i.e. into a region of higher velocity, so that in this manner an exchange of pulses takes place, which has a particularly disadvantageous effect on the flow resistance. The velocity distribution at a "slow band" is moreover especially unstable, and this is a source of strong fluctuations which maintain the turbulence of the boundary layer. The transverse flow which leads to the formation of the "slow bands" can be obstructed by the known fine longitudinal grooves. The effect is the better, the more sharp-edged is the construction of the ridges of the ribs disposed between the grooves. In this manner, it is even possible to achieve a reduction in resistance which is of the order of magnitude of 8%.